1. Field of the Invention
The present invention relates to area lighting fixtures and systems such as streetlights for highways, roads, walkways and other public areas, as well as porch, security, and garden lights for private outdoor uses. Alternatively, the fixtures and system can be used for indoor lighting such as that used in office buildings. The lighting fixtures and system uses discrete energy-saving light sources, such as LEDs, and a method for automatically adjusting the light and energy output based on the amount of ambient light available to light the intended target area. Streetlights, for example, inversely resonate with the amount of ambient moonlight, thus dimming and brightening each month as the moon cycles through its phases. The utilization of available ambient light to adequately illuminate the target surface saves energy, mitigates light pollution, and intensifies the urban experience of moonlight.
2. Description of Related Art
A great deal of energy is wasted on lighting fixtures and systems which do not take into account the amount of ambient light available to adequately light the target area. Current fixtures and systems allow for a user to turn a light on or off (or even dim a light) depending on the desired need for lighting. But, energy saving lighting fixtures and systems are needed that take into consideration the available ambient light sources and adjust to the light and energy output according to need. Such systems would save significant amounts of energy and light pollution.
Current streetlights are prime examples of wasteful lighting fixtures and systems. Streetlight fixtures and systems produce an excessive amount of illumination to light the intended area, and such “over-illumination” may carry significant costs. For example, typical streetlights use a photocell to turn on at dusk and off at dawn. This practice ignores differences in ambient light levels at night, specifically moonlight. Moonlight varies from 0 lux at a new moon, to 0.35 lux at a full moon. This is a sufficient amount of light for vision in many areas. Therefore, changing the output of streetlights in inverse proportion to ambient moonlight offers the opportunity to save energy. It also enables an aesthetic appreciation of moonlight in urban areas, where this is currently not possible due to light pollution.
Streetlights account for as much as 8% of electricity used in the United States. The cost to produce this amount of electricity is enormous, and it is estimated that the energy production to light streetlamps results in approximately 3,000,000 tons of carbon emissions per year. Current streetlight fixtures and systems also have negative safety and aesthetic impacts. Glare and haze from over-illumination contribute to road accidents and decrease urban populations' ability to experience stars or moonlight on a nightly basis.
The following facts are pertinent to the background of the invention:
1) Moonlight is only 100,000th as bright as sunlight. Therefore, a moonlight sensor must be much more sensitive than those used in conventional streetlights.
2) Conventional streetlight photosensors detect ambient light levels, and do not need to measure direct sunlight. Moonlight, however, is sufficiently dim that accurate sensing requires that the sensor be pointed directly at the moon. However, the moon moves through a wide orbital arc each night, so that a typical flat sensor oriented in one direction will receive inaccurate readings due to the changing angle of incidence, depending on the relative position of the moon.
3) A photoreceptor of the necessary sensitivity will be affected by ambient cloud glow from light pollution. At low angles, it may also be affected by direct light from sources such as conventional streetlights and building lights. This is problematic because at low light levels, diffuse, non-directional light is less effective for human vision than direct, shadow-casting light, such as moonlight.
4) Typical High Intensity Discharge lamps used for streetlights do not dim continuously or efficiently.
While it is possible that the energy output for lighting fixtures and systems can be controlled manually (with a dimmer switch for example), such manual switching is often impractical and inefficient. Manual dimming of lighting systems requires the expenditure of significant man hours to collect data relating to the amount of ambient light that is available and to control the dimmer accordingly. Further, dimming an entire system would be ineffective because not every light in a particular system is targeting an area with the same amount of available ambient light. Such ambient light changes can vary spatially and in unpredictable ways. For example, when a cloud passes over a certain area of the lighting system, the lights under the cloud may need to project more light than those that are not under the passing cloud and, even then, the passing cloud would only affect the lighting efficiency of a certain number of lights for a certain period of time.
It is also possible to control energy output for lighting fixtures and systems by using an automatic timer. For example a timer could be set at the source location of the energy output to provide enough energy to coincide with a predicted timed transition of light from sunlight to moonlight and with the expected ambient light output associated with a certain time of year or cycle of the moon. But that system would be limited in that it would likely be unable to detect the specific needs of a certain number of lights on the system depending on positioning of those lights and the changing weather or light producing conditions.
The following is a partial list of the objects and advantages of the present invention: It is an object of the present invention to provide street lighting fixture and system that will sense the amount of ambient light and adjust the power output according to the amount light needed to adequately illuminate the desired target area. It is another object of the present invention to utilize relatively low voltage and adjustable luminaries, such as LEDs, to provide the needed light output. It is another object of the present invention to provide an area lighting fixture that can retro-fit existing streetlight fixtures so as to not detrimentally affect the purposes for which the existing streetlights have been designed, such as staying within an appropriate wind load. It is an object of the present invention to provide an area lighting device that provides a light output that minimizes the occurrence of light pollution. It is an object of the present invention to provide an area lighting device that allows for the maximum use of ambient light, such as moonlight, to illuminate the target area.
It is an object of the present invention to reduce the energy waste and high maintenance cost associated the current lighting fixtures and systems. It is an object of the present invention to present an adaptable, variable lighting fixture and system which takes practical advantage of natural ambient lighting cycles, but celebrates their experiential power.
It is an intention of the invention to present a system utilizing currently available, “off the shelf” and reasonably priced technology that could quickly pay for itself through energy cost savings.
It is an intention of the present invention to achieve technical and operational simplicity.
It is an intention of the present invention to profoundly alter the aesthetics of city life by enhancing the natural lighting of city streets. It is an intention of the present invention to inspire new cycles of culture and urban life—moonlight walks, performances, festivals, weddings and outdoor parties and, thus forge a new urban connection to nature which is temporal rather than spatial.